Rapid fabrication of stable and highly transparent superhydrophobic glass surfaces using femtosecond laser double-pulse trains

Achieving superhydrophobic surfaces with high optical transparency and durability remains a key challenge for optical and fluidic applications. This study investigates the formation mechanism of femtosecond laser-induced microgroove arrays and compares three double-pulse configurations—low–high, equal–equal, and high–low energy sequences—with the conventional single-pulse mode for generating hierarchical micro/nanostructures. Among them, the low–high sequence (Type 1) produced the most uniform and defined structures by modulating free-electron dynamics and enabling homogeneous energy deposition, stabilizing a Cassie–Baxter wetting regime. A 1.5 × 1.5 cm² transparent superhydrophobic sample was fabricated in 75 s using a single scan, maskless process. After applying a fluorocarbon plasma treatment (C₄F₈), the Type 1 surface showed a water contact angle of 154.5° and high transmittance (>88%) in the 300–800 nm range. XPS revealed the highest CF₂/CF₃ ratio on this surface, correlating with enhanced hydrophobicity. The surface also demonstrated excellent durability against compression, tape delamination, aging, water jets, thermal cycling, and chemical corrosion. This work presents a rapid and scalable laser-based method for fabricating large-area, durable, and transparent superhydrophobic glass surfaces for potential use in optical windows, self-cleaning coatings, microfluidics, and smart devices.